Cracking of tertiary aliphatic hydroxy compounds to produce acetylenic hydrocarbons



CRACKING OF TERTIARY ALIPHATIC HYDROXY COMPOUNDS TO PRODUCE ACETYLENICHY- 5 DROCARBONS John Happel, Yonkers, and Charles J. Marsel, New York,N. Y.

No Drawing. Application September 29, 1952, Serial No. 312,158

8 Claims. (Cl. 260-'678) This invention relates to novel processes forthe production of acetylenic hydrocarbons together with diolefins by thethermal cracking of tertiary aliphatic alcohols, and more particularly,it relates to a novel method for making methyl acetylene by the crackingof tertiary butyl alcohol.

The commercial production of acetylenic hydrocarbons is generally basedon relatively complicated and expensive methods involving chemicalsynthesis procedures. For example, the simplest member of the acetylenichydrocarbon series, acetylene itself, is the most widely known and usedof the acetylenic compounds. Practically all the present commercialproduction ismade by the relatively expensive method of reacting waterwith calcium carbide CaCz. Homologs and derivatives of acetylene itselfare more difiicult and expensive to make and for this reason have notbeen made available commercially.

Methyl acetylene has been produced by the reaction of water withmagnesium carbide, MgzCs. Higher acetylenes are also produced bydehydrohalogenation reactions, such as methyl acetylene fromdibromopropane, and diacetylene from dichlorobutyne. Pyrolysis has alsobeen employed using the arc process or other types of high temperatureand short time of contact cracking techniques to produce acetylenes fromlow molecular weight hydrocarbons. However, all present methods forproducing higher acetylenes are relatively expensive techniques, orproduce acetylenes in poor yields. These difficulties are intensified incommercial scale operations.

It has been discovered that low molecular weight substituted acetylenescan be made in good yield and purity by the thermal cracking of lowmolecular weight tertiary alcohols and glycols in the presence of steamunder conditions of high temperatures and low contact time of the feed.In some cases, under controlled conditions, valuable diolefins are alsoproduced. There is no coking of the equipment, and consequently no lossof the feed stock in such useless materials. It has further beendiscovered that steam has a unique and hitherto unknown ability to aidthis reaction by cutting down tar formation and greatly facilitating theformation of the desired acetylenic products.

Thus the procedure of the invention has a number of advantages overpresent cracking techniques. The tertiary alcohols, being liquids, areeasily handled and pumped. The use of steam during the cracking stepavoids the formation of carbon and tars without the use of vacuum orother tedious variations. In addition, tests have indicated that thealcohol cracks much more readily and cleanly than the correspondingolefin, using the same mole ratios of steam and the same crackingconditions. 60

To summarize, the appropriate tertiary alcohol is mixed with the properamount of water or steam, vaporized and passed into a cracking zone,where it is exposed to high temperature and short time of contact,suitably adjusted for the exact compound to give the optimum yield of 70desired acetylenic product. The mixture is rapidly ice quenched by wateror steam, injection and the products separated by the usual techniques.The feed stock to be used is selected from the group of aliphatictertiary alcohols and glycols characterized by the following structuralgroup:

GHa

HrC- H They are pyrolized in the presence of steam, at atmospheric orslightly higher pressures to yield an acetylenic hydrocarbon. Thusgenerically:

CH: arc-n- H In the case of tertiary butyl alcohol, for example,

CH1 CHaC-CH3 CHsCECH V or with methyl but'ynol CH3 1 onrnozon *Q nozoozoH Contact times of less than 1 second employed in conjunction with atemperature within the range of 800 to 900 C. are necessary for the bestand most efiicient operation of the process. In general, best yields andconversion are obtained by a correlation of contact'time andtemperature, such that the longer the contact time, the lower thetemperature which is used. Conversely, the shorter the contact time, thehigher the temperature which can be tolerated. Substantially atmosphericpressures are employed for best results although pressures higher thanatmospheric can also be used. Steam should be employed admixed with. thetertiary alcohol feed in mole percent concentrations of more than 50%and preferably in the range of to mole percent.

The feed can be the pure tertiary alcohol or glycol or a mixturecontaining substantial amounts of the appropriate feed can also be used,provided no materials are present which will interfere with the reactionor unduly contaminate the product.

Among the compounds Which may be employed as feeds and which shouldcontain in the molecule at least one tertiary hydroxyl group areincluded the following:

CH3 CH Om n-0H; CHa- -CECH H H Tertiary Butyl Alcohol Methyl Butynol CH3CH CH3 CH3 CHaN CHs CH3( /C CCCHa OH H OH H Pinaeol Dimethyl HexynediolThe operation may be carried out in a pyrolysis tube or a series oftubes or coils made of stainless steel, quartz or the like. Also brickcheckerwork or stoves of the type used for pyrolysis may be used. Suchstoves commonly use the principle of regenerative cooling for economy ofoperation.

This novel process is particularly valuable for producing methylacetylene and mixtures of methyl acetylene with allene from mixturescontaining relatively large amounts of tertiary butyl alcohol.Conditions which are especially adaptable for making methyl acetyleneare 800-900 C. and .005-5 seconds contact time and 80-90 mole percentsteam. f

In order to achieve controlled low time of contact, it is necessary tocool the cracked gases very quickly to at least 500 C. after they leavethe thermal cracking zone. Shock or quick cooling of the cracked gasesserves two purposes. Firstly it serves to bring the temperature of thereacted gases quickly below the pyrolytic temperature in order to keepdecomposition of product and secondary reactions to a minimum andsecondly, it reduces the temperature of the methyl acetylene to lowertemperatures at which polymerization reactions are at a minimum. Thesetwo objectives may be accomplished by shock cooling of the crackedgases. A direct water quench may be placed immediately after the heatingzone. The gases may be passed directly into a stream or spray of coldwater or oil. Cool gases may be mixed with the exit gases immediatelyafter they leave the heating zone. The substituted acetylene isseparated by condensation of the steam, further compression to knock outadditional water, and subsequent pressure distillation to separatemethyl acetylene and allene from the reaction products. Recoveredisobutylene is recycled back to the cracking coil.

Example I A solution containing mole percent of tertiary butyl alcoholand 90 mole percent of water was vaporized, preheated to above 200 C.and passed through a stainless steel cracking tube furnace. Athermocouple probe in the cracking tube gave a temperature profile overthe length of the tube of about 850-900 C. Contact time in the furnaceWas approximately .05.5 second. Product was then quenched with steam.Upon analysis of the reaction mixture, it was found that 5.9 molepercent of the tertiary butyl alcohol was converted to methyl acetylene.Approximately an equal amount of allene was found. The remainingreaction product consisted of isobutylene from unreacted butanol,methane, hydrogen, and small amounts of other hydrocarbons.

Example 2 A solution containing approximately 110 mole percent of methylbutynol and 90 mole percent of water was vaporized, preheated to about200 C. and passed through a cracking tube furnace with a temperature ofabout 850900 C. The product was quenched with nitrogen gas, and analysisof the reaction mixture proved the presence of diacetylene.

The production of methyl acetylene is of especial importance, since thischemical compound has unique properties which make it useful as acombustible fuel for welding operations and jet engines, and as achemical intermediate.

What is claimed is:

l. A process for the production of acetylenic compounds which comprisessubjecting a feed containing substantial amountsof a compound possessingat least one aliphatic tertiary hydroxyl group and at least mole percentof steam to temperatures of from 800 to 900 C., at a contact time ofless than 5 seconds.

2. A process for the production of acetylenes and other products whichcomprises subjecting a feed containing a compound possessing at leastone aliphatic tertiary hydroxyl group and in the presence of at least 50mole percent of steam, to temperatures of from 800 to 900 C. at acontact time of less than 5 seconds.

3. A process for the production of methyl acetylene which comprisessubjecting a feed containing tertiary butyl alcohol and at least 50 molepercent of steam, to temperatures of from 800 to 900 C. at a contacttime of less than 5 seconds.

4. A process for the production of a mixture of methyl acetylene andallene which comprises subjecting a feed mixture containing tertiarybutyl alcohol and at least 50 mole percent of steam based on the alcoholto a thermal cracking at a temperature within the limits of 800 to 900C., and at a contact time of .005 to 5 seconds.

5. A process which comprises subjecting a mixture of tertiary butylalcohol and from to mole percent of steam, to a thermal cracking at atemperature within the limits of 800 to 900 C., and at a contact timeof' less than 1 second and isolating methyl acetylene from the resultantcracked gases.

6. A process which comprises subjecting a mixture containing from 10 to20 mole percent tertiary butyl alcohol and from 90 to 80 mole percentsteam to a cracking step at a temperature in the range of 800 to 900 C.,and a contact time between .005 and 5 seconds and isolating methylacetylene from the resultant cracked gases.

7. A process for making a cracked mixture containing substantial amountsof methyl acetylene and allene which comprises preheating a mixturecontaining 10 mole percent tertiary butyl alcohol and 90 mole percentsteam, passing said mixture to a cracking zone in which it is sub.-jected to a temperature of 800 to 900 C. for a period of less than 1second, quenching the hot cracked mixture and isolating methyl acetylenefrom the cooled gases. 8. A process for making a cracked mixturecontaining substantial amounts of diacetylene which comprises preheatinga mixture containing 10 mole percent methyl butynol and 90 mole percentsteam, passing said mixture to a cracking zone in which it is subjectedto a temperature of 800 to 900 C., quenching the hot, cracked mixture,and isolating diacetylene from the cooled gases.

References Cited in the file of this patent UNITED STATES PATENTS1,986,876 Baxter et al. Jan. 8, 1935 2,429,566 Rice Oct. 21, 19472,524,866 Winslow Oct. 10, 1950

1. A PROCESS FOR THE PRODUCTION OF ACETYLENIC COMPOUNDS WHICH COMPRISESSUBJECTING A FEED CONTAINING SUBSTANTIAL AMOUNTS OF A COMPOUNDPOSSESSING AT LEAST ONE ALIPHATIC TERTIARY HYDROXYL GROUP AND AT LEAST50 MOLE PERCENT OF STEAM TO TEMPERATURE OF FROM 800* TO 900* C., ACONTACT TIME OF LESS THAN 5 SECONDS.